Highly purified interferon, which is a very interesting substance and is being investigated throughout the world, is today available for medical research only in very small amounts. Therefore, it has heretofore not been possible to subject interferon-proteins to structural or biochemical investigations. Since the N-terminal sequence of human lymphoblast-interferon has now been elucidated [Science 207, 525-526 (1980)], the tridecapeptide of the instant invention has for the first time been synthesized and its properties investigated.